Are all cards that have appeared in a booster expansion technically legal in any format where Unhinged is legal because Booster Tutor exists?
Here’s how it works. Silver border is a toggle that you can add to formats. Un-Modern is a format allowing Modern cards and any silver bordered cards (which includes holiday cards and other silver-bordered promotional cards). That means that Richard Garfield PhD can only copy Modern and silver-bordered cards in that format.
Now here’s where things get interesting. When you Booster Tutor in a booster pack, one of the side effects of the Booster Tutor is it adds that whole set to the format for that game.
So Booster Tutor in an Alpha booster and now, for the remainder of the game, Richard Garfield can turn a card that cost U into an Ancestral Recall or one that costs 1U into a Time Walk. (Only once though as Richard doesn’t let you choose the same card twice.)